This invention relates to improved methods and systems for the metallization of semiconductor devices such as integrated circuits, memory cells, and the like that use copper metallization; more specifically this invention relates to methods and systems for copper-based metallization of silicon integrated circuits.
An important part of the fabrication of semiconductor devices is the metallization of the devices to electrically interconnect the device elements. For many such devices, the metallization of choice includes the use of copper metal lines. Metallization systems that use copper metal lines also must use a barrier material to isolate the copper from copper sensitive areas of the electronic devices. Some of the barrier layers of interest for copper metallization are materials such as tantalum and such as tantalum nitride. The usual fabrication process for metallization systems that use copper involves the deposition of copper onto the barrier layers. A preferred process for depositing the copper onto the barrier layer is electroless copper deposition.
One problem that occurs for the standard technology used for copper metallization is that many of the preferred barrier materials such as tantalum and tantalum nitride, if exposed to air for extended periods of time, can form oxides such as tantalum oxide and tantalum oxynitride on the surface of the barrier layer. It is known that electroless deposition of copper onto the barrier layer is inhibited if there is oxide present on the barrier layer. In addition, copper does not adhere to the oxide on the barrier layer as well as it adheres to the pure barrier metal or metal rich barrier layer surface, such as tantalum and tantalum-rich surface on tantalum nitride. Tantalum and/or tantalum nitride barrier layers are only presented here as examples; similar problems occur for other barrier layer materials. The poor adhesion can negatively affect the electro-migration performance and reliability of the semiconductor devices. In addition, the formation of tantalum oxide or tantalum oxynitride on the barrier layer surface can increase the resistivity of the barrier layer. More specifically, the presence of the oxide between the barrier layer and the composite copper can reduce the performance for the electronic devices and reduce the reliability of the electronic devices fabricated using standard copper metallization technology.
Clearly, there are numerous applications requiring high-performance high reliability electronic devices. The problems that occur for the standard technology for fabricating electronic devices using copper metallization indicate there is a need for methods and systems that can allow the fabrication of electronic devices using copper metallization with improved performance and improved reliability.